JP2015173500A - Radio communication system and radio communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio communication device and a radio communication system which are able to set a modulation scheme and a modulation constant optimal to the propagation environment of each terminal in communication with a communication terminal in a different radio wave propagation environment.SOLUTION: A radio communication device includes: first communication means for performing at least one of transmission or reception by use of a multicarrier signal comprised of a plurality of subcarriers shaped by a band-limited pulse waveform; and second communication means for performing at least one of transmission or reception by use of a signal by a modulation scheme or a modulation constant different from the first communication means. The first communication means performs communication without using at least one of the plurality of subcarriers, and the second communication means is characterized by performing communication by use of the band of a subcarrier the first communication means does not use.

Description

  The present invention relates to a wireless communication system and a wireless communication apparatus.

  In recent years, wireless communication systems with relatively short distances such as wireless LANs have become widespread, and transmission speed has been increased. In general, when the transmission speed is increased, the transmission characteristics are affected by delay spread due to multipath propagation, and the transmission characteristics are deteriorated. To solve this problem, multi-carrier transmission by OFDM (Orthogonal Frequency Division Multiplexing) is used in wireless LAN and terrestrial digital television broadcasting. Multicarrier transmission is frequency multiplex transmission using a plurality of modulated subcarriers, and a modulation signal is generated by inverse fast Fourier transform (IFFT). Therefore, all symbols are synchronized, and modulation of all subcarriers is the same symbol. Rate.

  In the OFDM transmission signal, a section called a guard interval (GI) is added to the beginning of the modulation symbol. Since a copy of the trailing edge portion of the transmission symbol waveform is arranged in this section, it is also called a cyclic prefix (CP). If the multipath delay spread is less than or equal to the GI length, delay distortion can be compensated. However, for delay spread exceeding the GI length, errors during data demodulation increase and the characteristics deteriorate. When the GI is lengthened, a good error rate characteristic can be obtained even when the delay spread is large, but the data rate is lowered because the OFDM symbol length becomes long. Therefore, in OFDM, it is common to design a communication method with a minimum required GI length corresponding to the delay spread assumed in the propagation path (transmission path), that is, the impulse response length of the transmission path characteristic. This GI length is normally fixed, and a common value is used for all terminals in a communication system that performs multiple access including a master station (base station) device and a slave station (terminal) device. In the case of a communication system using time division multiple access (TDMA), it is possible to switch the GI by time for each time slot. However, in TDMA, the modulation speed, that is, the symbol clock becomes high, and the transmission delay is proportional to the TDMA frame length Therefore, it is not a general technique for solving the above-mentioned problem because there is another problem that it becomes longer.

  Further, the spectrums of OFDM subcarriers overlap each other, and even if the amplitude of a specific subcarrier is 0, the spectrum of the adjacent or next adjacent subcarrier is superimposed on the frequency of the subcarrier. For this reason, if there is another wireless communication with a relatively narrow band at a certain frequency, it is difficult to avoid interference even if the amplitude of the subcarrier corresponding to that frequency is zero. In order to solve this problem, Patent Document 1 and Non-Patent Document 1 propose a multicarrier transmission scheme in which subcarriers are band-limited by a Gaussian function, and experimental results are disclosed. By shaping the transmission waveform with a Gaussian function, steep spectral attenuation characteristics can be given, and intersymbol interference and intersubcarrier interference within the system and radio wave interference with other systems can be suppressed.

JP 2005-236364 A

Tetsuo Ohori, Junichi Onodera, Kenji Gojima, Takeshi Terao, Jun Suyama, Hiroshi Suzuki, “Evaluation of feasibility of Gaussian multicarrier transmitter by FPGA implementation”, IEICE technical report, RCS2007-220, pp.205- 210, Mar.2008

  In the above prior art, for example, when performing frequency division multiple access (OFDMA) by OFDM such as WiMAX (IEEE802.16 standard), all subcarriers are collectively processed by FFT and IFFT (fast Fourier transform, inverse fast Fourier transform). Then, modulation / demodulation signal processing is performed. Therefore, the GI length cannot be set to another value for a specific subcarrier. For this reason, it is necessary to design the GI length in accordance with the maximum delay spread, and an unnecessarily large GI is used even for a slave station in a propagation path state where the delay spread is small, and unnecessary frequency resources are wasted. Will be.

  In order to change the GI length, the symbol rate, etc. for each subcarrier, it may be possible to provide two different modulation / demodulation means. That is, in addition to modulation / demodulation means for performing modulation / demodulation of OFDM, it is conceivable to provide another modulation / demodulation means with different modulation constants such as GI and symbol rate or independent in a completely different modulation format in the master station apparatus. However, since the spectrums of the signals by the respective modulation / demodulation means are overlapped and GI is different, these signals are not orthogonal to each other. Therefore, interference occurs between the respective signals, and the bit error rate is greatly increased and cannot be put to practical use.

  A wireless communication system in a vehicle can be given as an example in such an environment that requires different GIs depending on subcarriers. In recent years, communication between in-vehicle devices is increasingly performed by wireless connection instead of wired connection. There are various environments in the vehicle, and the engine room surrounded by metal is likely to reflect radio waves and the delay spread becomes large. Therefore, GI is used for communication between in-vehicle devices installed in the engine room. It is necessary to take big. Furthermore, since the in-vehicle device installed in the engine room and the in-vehicle device placed in the vehicle compartment are shielded by metal, there is no direct wave and the delay spread is large, so a large GI is required as in the engine room. It becomes. On the other hand, the propagation path between the in-vehicle devices placed in the vehicle interior does not have a large delay spread, and the GI can be reduced.

  Furthermore, since a slave station that performs OFDMA requires OFDM modulation / demodulation, the configuration is complicated, and it is difficult to apply to a slave station device that can implement only single carrier low-speed transmission, such as a small sensor terminal. For example, a sensor node mounted on a vehicle is often required to be small and inexpensive, and it is difficult to provide an OFDM modulator / demodulator.

  In addition, since the OFDM subcarrier has an occupied bandwidth several times the subcarrier interval, if there is another wireless communication with a relatively narrow band at a specific frequency, the subcarrier corresponding to the frequency Even if the carrier amplitude is 0, interference cannot be avoided. Therefore, it is necessary to assign subcarriers from frequencies that are sufficiently away from frequencies used by other wireless systems. For these reasons, the communication system according to the above prior art has a problem that it is difficult to operate in an ISM (industrial science and medical) band such as a 2.4 GHz band in which various wireless systems are mixed.

  The present invention has been made in consideration of the above problems, and its purpose is to set the most suitable modulation method and modulation constant for the propagation environment of each terminal in communication with communication terminals in different radio wave propagation environments. And a wireless communication system are provided.

  In order to achieve the above object, the wireless communication apparatus according to the first embodiment of the present invention is most suitable for the propagation environment of each terminal in communication with communication terminals in different radio wave propagation environments by the following means. Modulation method and modulation constant can be set.

A wireless communication apparatus according to a first aspect of the present invention is a first communication unit that performs at least one of transmission and reception using a multicarrier signal composed of a plurality of subcarriers shaped by a band-limited pulse waveform. And second communication means for performing transmission or reception using a signal having a modulation format or modulation constant different from that of the first communication means,
The first communication means performs communication without using at least one of the plurality of subcarriers, and the second communication means is not used by the first communication means. Communication is performed using a subcarrier band.

  By shaping the transmission waveform with a band-limited pulse waveform, a steep spectral attenuation characteristic can be obtained. That is, since a spectrum dip can be formed deeply and inter-carrier interference can be reduced, by creating a subcarrier (null carrier) that is not used for communication, other communication is performed using the null carrier band. It can be performed. Since communication in this band does not interfere with multicarrier communication, the modulation format and modulation constant can be freely set according to the function of each terminal, the assumed delay spread of the transmission path, and the like. It can be accommodated simultaneously with communication.

  The subcarrier symbol used by the first communication unit may be asynchronous with the carrier symbol used by the second communication unit.

  By shaping the transmission waveform with a band-limited pulse waveform, interference between subcarriers can be minimized. That is, since the signal modulated by the first communication means and the signal modulated by the second communication means can be communicated even if they are not orthogonal, both symbols can be made asynchronous.

The first communication unit performs communication without using two or more subcarriers of the plurality of subcarriers, and the second communication unit includes the first communication unit. Communicates the same signal in the frequency bands of subcarriers not used for communication, weights signals in each frequency band and transmits them, or selects and transmits signals in any frequency band It is good.

  By configuring in this way, it is possible to transmit a plurality of carriers modulated by the same data, so that it is possible to obtain a frequency diversity effect for dealing with frequency selective fading. Further, it can be operated with a single transmission antenna, and the apparatus can be miniaturized.

In addition, the second communication means weights and transmits the signals of the plurality of frequency bands so that the signals of the plurality of frequency bands have the same phase at the antenna input of the transmission destination terminal. Alternatively, the second communication means may transmit signals in three frequency bands fc + fd, fc, and fc−fd having the same frequency interval.

  By equalizing the intervals of a plurality of transmission frequencies and transmitting in the same phase, it is possible to demodulate the received signal without performing complicated calculations at the transmission destination terminal.

  The first communication unit performs communication without using two or more subcarriers of the plurality of subcarriers, and the second communication unit includes the first communication unit. Transmitting to a plurality of terminals using transmission signals in frequency bands of subcarriers not used for communication, weighting and combining data addressed to the plurality of terminals based on propagation path characteristics, The transmission signal may be determined, and the second communication means may perform weighting so that data addressed to the terminal is dominantly received at the antenna input of the plurality of terminals. May be a feature.

  With this configuration, spatial multiplexing transmission can be performed with a single transmission antenna, and frequency use efficiency is improved. In addition, since the transmission destination terminal does not require signal separation processing, the apparatus can be simplified.

  The first communication unit performs communication without using two or more subcarriers of the plurality of subcarriers, and the second communication unit includes the first communication unit. A signal is received using a frequency band of a subcarrier not used for communication, and in each frequency band, a signal of the same data is transmitted from a transmission source, and the second communication means Each frequency band signal may be weighted and received, or one of the frequency band signals may be selected and received.

  By configuring in this way, the frequency diversity effect by transmitting the same signal at a plurality of frequencies can be obtained even during reception.

  The first communication unit performs communication without using two or more subcarriers of the plurality of subcarriers, and the second communication unit includes the first communication unit. It receives signals from a plurality of terminals using frequency bands of subcarriers not used for communication, and each of the plurality of terminals transmits signals in a plurality of frequency bands. A signal transmitted from each terminal may be extracted by weighting and combining received signals based on propagation path characteristics.

  By configuring in this way, it is possible to obtain the effect of improving the frequency use efficiency by spatial multiplexing transmission at the time of reception.

  The wireless communication apparatus according to the second aspect of the present invention is inputted with receiving means for receiving signals of a plurality of frequency bands transmitted from the second communication means included in the wireless communication apparatus according to the first aspect. Frequency conversion means for converting the frequency of the signal, wherein signals of a plurality of frequency bands received by the receiving means are converted into a common frequency band by the frequency conversion means.

  By configuring in this way, it is possible to receive signals transmitted by a plurality of frequencies by the receiving means for receiving a single frequency, and thus the apparatus configuration can be simplified.

  In addition, the wireless communication device according to the second aspect of the present invention receives the signals in the frequency bands fc + fd, fc, and fc−fd transmitted from the second communication unit of the wireless communication device according to the first aspect. Means and a frequency conversion means for frequency-converting an input signal, wherein an input signal, a signal obtained by frequency-converting the input signal by frequency + fd, and a signal on which a signal obtained by frequency-converting the input signal by frequency -fd are superimposed. It is preferable that the frequency conversion means output, and the reception means superimposes and adds the signals of the frequency bands fc + fd, fc, and fc−fd to the frequency band fc by the frequency conversion means.

  With this configuration, it is possible to receive signals from a plurality of frequency bands with a simple configuration in which frequency conversion means is added to a normal single carrier transmission / reception circuit.

A radio communication system according to the present invention is a radio communication system including a master station device, one or more multicarrier terminals, and one or more single carrier terminals, wherein the master station device A first communication means for communicating with a multicarrier terminal using a multicarrier signal comprising a plurality of subcarriers shaped by a band-limited pulse waveform, and a modulation format or modulation different from the first communication means Second communication means for performing communication using a signal by a constant, the multicarrier terminal has communication means for communicating with the first communication means of the master station device, and the single carrier terminal is A communication unit that communicates with the second communication unit of the master station device, and in communication between the master station device and the multicarrier terminal, the number of subcarriers is small. Communication is performed without using at least one, and communication between the master station device and the single carrier terminal uses a subcarrier band that is not used for communication between the master station device and the multicarrier terminal. And communicating.

  With this configuration, a wireless communication system can be constructed by the wireless communication device according to the first aspect of the present invention and the wireless communication device according to the second aspect.

  The radio communication system according to the present invention is a radio communication system including a master station device and a plurality of terminals, and the master station device uses a plurality of frequency band signals to transmit to the plurality of terminals. Transmission means for weighting and synthesizing data addressed to the plurality of terminals based on propagation path characteristics, and determining a transmission signal of each frequency band, wherein the terminal is a transmission means of the master station The transmission unit of the master station device may receive data addressed to the terminal at the antenna input of the plurality of terminals. May be characterized by being weighted so as to be received dominantly.

  The radio communication system according to the present invention is a radio communication system including a master station device and a plurality of terminals, each of which transmits a signal to the master station device using a plurality of frequency bands. And transmitting means, wherein the plurality of frequency bands are common to the plurality of terminals, and the master station device weights and combines signals received in the plurality of frequency bands based on propagation path characteristics. Then, it may be characterized by having receiving means for extracting a signal transmitted from each terminal.

  With this configuration, it is possible to construct a wireless communication system that can perform multiplex transmission at different frequencies using a single antenna.

  According to the present invention, it is possible to provide a radio communication apparatus and a radio communication system capable of setting a modulation method and a modulation constant most suitable for the propagation environment of each terminal in communication with communication terminals in different radio wave propagation environments. .

It is a functional block diagram of the radio | wireless communication apparatus which concerns on this invention. It is a figure explaining the subcarrier shaped by the Gaussian pulse. It is a figure explaining the shaping method of the subcarrier by a Gaussian pulse. It is the figure which has arrange | positioned another carrier and symbol to the null carrier of multicarrier communication. It is a figure explaining the structure of the multicarrier modulation signal generation part which concerns on 1st embodiment. It is a figure explaining the structure of the single carrier modulation | alteration signal production | generation part which concerns on 1st embodiment. It is a figure explaining the structure of the multicarrier demodulation part which concerns on 1st embodiment. It is a figure explaining the structure of the single carrier terminal which concerns on 1st embodiment. It is a figure explaining the terminal structure of the radio | wireless communications system which concerns on 2nd embodiment.

(First embodiment)
<System configuration>
FIG. 1 is a diagram illustrating a system configuration of a wireless communication system.
This system is also called a base station device, also called a base station, access point, parent device, or sink node, and a terminal, slave device, sensor node, etc., in a relatively short distance space such as indoors, in a vehicle, or in a device. Wireless transmission is performed with a slave station. The master station device performs multiple access with a plurality of slave stations.

  This system includes a master station device B, a multi-carrier terminal TM and a single carrier terminal TS which are slave station devices. Here, a case where the master station device B communicates with two multicarrier terminals TM1 and TM2 and two single carrier terminals TS1 and TS2 will be described as an example, but how many slave station devices are there? It doesn't matter. Multi-carrier terminals have a higher transmission rate than single-carrier terminals. A single carrier terminal has a low transmission rate, but has a simple configuration and low power consumption. Such a single carrier terminal is suitable, for example, as a mounting form of a sensor terminal or the like that is limited in power source and requires small and low power consumption.

  In this embodiment, in communication between a master station apparatus and a multicarrier terminal, multicarrier communication is performed without using one or a plurality of subcarriers among subcarriers that can be used for multicarrier communication. In communication between a master station device and a single carrier terminal, single carrier communication is performed using subcarrier frequencies that are not used for multicarrier communication.

The system configuration of the master station device B will be described.
The master station apparatus B in the first embodiment includes a multicarrier modulation signal generation unit 111, a single carrier modulation signal generation unit 112, a D / A converter 113, and an amplifier 114, and these units serve as transmission means. Configure. In addition, a multicarrier demodulator 121, a single carrier demodulator 122, an A / D converter 123, and an amplifier 124 are provided, and each of these parts constitutes a receiving means. Moreover, it has the spectrum control part 101, the antenna switching part 102, and the antenna 103 which are common to a transmission and reception means.

  Each configuration will be described. The multicarrier modulation signal generation unit 111 is means for converting the input digital signal sequence to be transmitted into a modulation signal having a plurality of carriers. More specifically, transmission data is converted into parallel data, primary modulation is performed on each data, inverse Fourier transform (IFFT) is performed to generate a plurality of subcarrier signals, and a band obtained by waveform shaping using Gaussian pulses. Synthesize after limiting. Details of band limitation by waveform shaping using a Gaussian pulse and the multicarrier modulation signal generation unit 111 will be described later. In this embodiment, multiple access by OFDMA is assumed, but multiple access may be realized by using TDMA or FDMA.

  The single carrier modulation signal generation unit 112 is a means for converting the input digital signal sequence to be transmitted into a single carrier modulation signal. Specifically, primary modulation is performed on transmission data, and band limitation is performed by waveform shaping using a Gaussian pulse. In the present embodiment, the same transmission data is transmitted at a plurality of different frequencies in order to obtain a frequency diversity effect. Details of the single carrier generation unit 112 will be described later. In this embodiment, QAM (Quadrature Amplitude Modulation) or QPSK (Quadrature Phase-Shift Keying) is assumed as the primary modulation method, but other modulation methods are used. It may be used.

  The modulation signal generated by the multicarrier modulation signal generation unit 111 and the modulation signal generated by the single carrier modulation signal generation unit 112 are combined and input to the D / A converter 113. A signal generation method and specific signal contents will be described later.

  The D / A converter 113 is means for converting a digital signal sequence, which is a generated baseband signal, into a radio frequency signal. The amplifier 114 is a power amplifier for amplifying the converted radio frequency signal. A band pass filter may be provided between the D / A converter 113 and the amplifier 114.

  The antenna switching unit 102 is a switch for electrically separating the transmission path and the reception path in order to share the antenna 103 for transmission and reception. This is realized by connecting a transmission filter having a reception frequency as a stop band and a reception filter having a transmission frequency as a stop band via a phase shifter.

  The A / D converter 123 is means for converting a radio frequency signal into a digital signal sequence. The amplifier 124 is a low noise amplifier that amplifies the radio frequency signal input to the A / D converter 123.

  The multicarrier demodulator 121 is a means for demodulating the multicarrier modulation signal into a digital signal sequence that is a baseband signal. The single carrier demodulator 122 is a means for demodulating the input single carrier modulated signal into a digital signal sequence that is a baseband signal.

  The spectrum control unit 101 is a means for determining a frequency used for communication with each terminal, that is, a spectrum. Details of the operation of the spectrum control unit 101 will be described later.

<Waveform shaping by Gaussian pulse>
Before detailed description of the master station device B, band limitation by waveform shaping using a Gaussian pulse will be described. A Gaussian pulse is a pulse signal using a Gaussian function, and has a property that both duration and bandwidth are limited. By multiplying this pulse signal and the carrier waveform, steep sidelobe attenuation can be obtained with respect to the frequency spectrum. FIG. 2 is a diagram comparing a frequency spectrum 202 (dotted line) that has been modulated by OFDM and a frequency spectrum 201 (solid line) that is the result of multiplication by a Gaussian pulse. The spectrum dip is about 10 dB in normal OFDM, but as a result of shaping with a Gaussian pulse, attenuation of 60 dB or more can be obtained.

  That is, by performing band limitation on a subcarrier used in OFDM by waveform shaping using a Gaussian pulse, the influence on adjacent subcarriers or symbols can be minimized. It is known that the inter-symbol interference is reduced by reducing the standard deviation σ of the power in the time direction of the Gaussian pulse used for shaping, and the inter-carrier interference is reduced by increasing it. As the standard deviation σ, any value may be used as long as the object of the invention can be achieved.

FIG. 3 is a diagram showing in detail a band limiting method using a Gaussian function. FIG. 3A shows three symbols of the signal subjected to the inverse Fourier transform. Of these, u ₀ (
An example in which band limitation is performed for a section t) will be described. The signal in FIG. 3A is multiplied by the following equation by the signal in FIG. 3C, which is a Gaussian waveform, and the sum of the three symbols is the target band-limited signal. . It is assumed that the Gaussian waveform is g (t), the input signal is u (t), the symbol length is Ts, and the range of t is 0 <t ≦ Ts.
g (t−Ts) u ₁ (t + Ts) + g (t) u ₀ (t) + g (t + Ts) u ₋₁ (t−Ts)
That is, the band-limited signal s (t) can be expressed by Equation 1. The truncation width of the Gaussian waveform is expressed by M × Ts, but in this example, M = 3. k is an arbitrary integer.

  When a plurality of terminals try to communicate with each other by a plurality of subcarriers by OFDMA, the spectrum of adjacent subcarriers overlaps, so that each carrier must have orthogonality. However, by using this method, adjacent subcarriers do not interfere with each other, and communication can be performed even if there is no orthogonal relationship, so there is no need to synchronize symbols. That is, a plurality of terminals can communicate at a plurality of symbol rates.

<Transmission carrier allocation method>
Next, a transmission carrier arrangement method will be described.

  When either the master station device or the slave station device starts communication, the spectrum control unit 101 assigns a frequency used for communication between each slave station and the master station, that is, a spectrum. More specifically, spectrum control section 101 determines a frequency allocated for communication between the multicarrier terminal and the parent station device and a frequency allocated for communication between the single carrier terminal and the parent station device. The determined frequency information is transmitted to multicarrier modulation signal generation section 111. Multicarrier modulation signal generation section 111 generates a modulation signal using this information. Multicarrier modulation signal generation section 111 does not allocate data to subcarriers of frequencies determined not to be used for multicarrier communication. That is, the amplitude of this subcarrier modulation output becomes zero. The frequency information determined by the spectrum control unit 101 is also transmitted to the single carrier modulation signal generation unit 112. The single carrier modulation signal generation unit 112 generates a modulation signal using this information.

  In this embodiment, a subcarrier determined not to be used for multicarrier communication is referred to as a null carrier. In addition, subcarriers that are not originally used for communication, such as DC subcarriers, are also referred to as null carriers.

  The frequency allocation can be performed as shown in FIG. 4, for example. In FIG. 4, the horizontal axis represents time and the vertical axis represents frequency. A white oval (symbol 400) indicates a symbol for each subcarrier of a modulated signal transmitted and received between the master station apparatus B and the multicarrier terminal TM. The ellipses with hatching indicate symbols for each subcarrier of the modulated signal transmitted and received between the master station apparatus B and the single carrier terminal TS.

  Here, T is the symbol length (symbol period) of the multicarrier modulation signal (the unit of time is second, and so on). As will be described in detail below, the multicarrier modulation signal is generated by inverse fast Fourier transform (IFFT), so that the subcarrier spacing is 1 / T (the unit of frequency is Hz; the same applies hereinafter) or an integral multiple thereof. . Here, the subcarrier interval is 1 / T. Further, fc is the center frequency of the multicarrier modulation signal.

The subcarrier frequency is given by the formula fc + m / T. Where m is an integer
When the number of points in IFFT (Inverse Fourier Transform) is N, the value satisfies −N / 2 ≦ m ≦ N / 2-1.

  In this embodiment, communication with a multicarrier terminal is performed using subcarriers other than m = 0, mf, and -mf. That is, in multicarrier communication, the amplitude of subcarriers m = 0, mf, and −mf is set to zero. The spectrum of these subcarriers not used by the multicarrier terminal is used for communication between the single carrier terminal and the master station apparatus. Here, an example in which the occupied bandwidth of the single carrier modulation signal is less than 1 / (2T) is shown. Therefore, the master station device 110 can perform single carrier communication with two single carrier terminals TS1 and TS2 using one null carrier band. The single carrier terminal TS1 uses subcarrier spectra of fc + 1 / (2T), fc + (mf + 1/2) / T, and fc− (mf−1 / 2) / T. The single carrier terminal TS2 uses subcarrier spectrums of fc-1 / (2T), fc + (mf-1 / 2) / T, and fc- (mf + 1/2) / T.

  Here, the symbol rate can be changed between multi-carrier communication and single-carrier communication because the modulation signal of multi-carrier communication is band-limited by waveform shaping using a Gaussian pulse as described above, causing inter-carrier interference. This is because there is not.

  In FIG. 4, three carriers are used in each single carrier communication, but in this embodiment, each of these carriers transmits a signal modulated with the same data. Therefore, since the same data is transmitted at three different frequencies, a frequency diversity effect is obtained and stable transmission is possible. Thus, the subcarrier and single carrier frequencies are arranged by the spectrum control unit so that the spectra do not overlap each other.

  In the present embodiment, description will be given below assuming that TDD (Time Division Duplex) communication is performed. Hereinafter, the carrier generated by the multicarrier modulation signal generation unit 111 is referred to as a high rate carrier, and the carrier generated by the single carrier modulation signal generation unit 112 is referred to as a low rate carrier.

<High rate carrier transmission method>
Next, a specific method for realizing the above-described carrier arrangement will be described.
First, a high rate carrier transmission method will be described. FIG. 5 is a configuration diagram of the multicarrier modulation signal generation unit 111. First, transmission data input for each communication partner is serial / parallel converted by converter 501 for each symbol of each destination multicarrier terminal. Here, the data M1 indicates data addressed to the multicarrier terminal TM1, and the data M2 indicates data addressed to the multicarrier terminal TM2. Then, subcarrier mapping section 502 assigns an appropriate subcarrier set for each communication partner in accordance with the frequency information transmitted from spectrum control section 101. The total number of assigned subcarriers is N or less. Here, N is the number of points of IFFT and is a power of 2. Subcarrier mapping section 502 does not assign data to subcarriers (character definitions will be described later) corresponding to fc ₁ and fc ₁ ± fd, fc ₂ and fc ₂ ± fd. That is, the amplitude of the modulation output for these subcarriers is set to zero.

  The signal divided into N subcarriers is subjected to, for example, QPSK or QAM modulation by a modulator 503 arranged for each subcarrier, and converted to a multicarrier modulation signal by an IFFT converter 504 having N points. .

The configuration up to here is the same as that of a conventional wireless communication apparatus using OFDMA. Therefore, the multi-carrier modulation signal is equivalent to a signal obtained by removing the guard interval from the conventional transmission signal by OFDM or OFDMA.

Next, the band limiting unit 505 performs filter processing using a Gaussian pulse for each subcarrier. The band limiting unit 505 is a convolution multiplication unit that multiplies one symbol of the impulse response of a filter that performs band limiting by waveform shaping using a Gaussian pulse. The band limiting unit 505 includes two delay units 506, three filters 507, and an adder 508. The delay unit 506 is a register or a memory and is a means for delaying one symbol. If u ₀ is used as a reference in the figure, u ₋₁ is OFDM signal data one symbol before and u ₁ is one symbol after. The filter characteristic in the filter 507 is preferably a Gaussian function as described above, but other functions such as a root cosine roll-off filter may be used. In this embodiment, filter processing, that is, truncation is performed using data for three symbols, but the number of processing symbols may be increased. By increasing the frequency, interference to adjacent subcarriers and channels can be further suppressed.

  The multicarrier modulation signal generated by the above processing is added by the adder 508. The same processing is performed for the other subcarriers, and the signals of all subcarriers are converted into serial data by the serial converter 509. Thereafter, it is added to the modulation signal of the low rate carrier and transmitted through a D / A converter and a transmission circuit.

  In high-rate carrier transmission, subcarriers are arranged by the method described above, and band limitation is performed on a transmission signal by a Gaussian function.

<Low-rate carrier transmission method>
Next, a low rate carrier transmission method will be described. FIG. 6 is a diagram illustrating the single carrier modulation signal generation unit 112 in more detail. First, modulation signal generation for the single carrier terminal TS1 will be described.

  The single carrier modulation unit 601 is means for performing normal single carrier modulation such as QPSK or QAM on input communication data. The band filter 602 is a unit that performs band limitation using, for example, a Gaussian function or a root cosine roll-off filter. By these processes, a baseband single carrier modulation signal similar to the conventional technique is generated.

  The generated single carrier modulation signal may have a modulation constant such as a symbol rate different from that of the above-described high rate carrier, that is, the multicarrier modulation signal. For example, in a transmission to a small and simple terminal such as a sensor terminal, transmission at a low bit rate is often good. Therefore, in this embodiment, the single carrier modulation signal is described as having a symbol rate of half, a symbol length of 2T, and an occupied bandwidth of about 1 / (2T), which is about half that of a high rate carrier. I do.

Next, the frequency conversion unit 603 converts the modulation signal addressed to the single carrier terminal TS1 into three frequencies so as to be fc ₁ -fd, fc ₁ , fc ₁ + fd in the baseband. Here, fc ₁ = fc + 1 / (2T) and fd = mf / T. These three signals are signals in which the same modulation is applied to the same data, and are different only in carrier frequency. The center frequency fc ₁ and the shift width fd are controlled so that the three converted frequencies coincide with the frequency of the null carrier received from the spectrum control unit 101. fc ₁ corresponds to 401b in FIG. 4, fc ₁ −fd corresponds to 401c, and fc ₁ + fd corresponds to 401a.

  The three signals converted by the frequency converter 603 are weighted and added by the adder 604. The weight used for the addition is determined by the propagation loss (transmission loss) of the above three frequencies, and a larger value may be set for a frequency with a small propagation loss, or all three may be output with equal amplitude. The weight used for the addition is a complex weight and involves phase control. That is, the three are controlled to have the same phase by the antenna input of the transmission destination terminal. The transmission characteristics of the transmission line may be measured by adding a training signal to the head of transmission data, as is well known in many wireless systems. Further, the transmission characteristics may be estimated by receiving and comparing the phases and amplitudes of the transmission signals of the three frequencies by the receiving circuit of the master station apparatus B. Note that the adder 604 may not only perform weighted addition, but may select only the frequency with the smallest propagation loss and stop outputting signals corresponding to other frequencies. In this case, the configuration and calculation are simplified.

A modulation signal is generated with the same configuration for transmission data addressed to the single carrier terminal TS2. The modulated signal addressed to the single carrier terminal TS2 is converted by the frequency conversion unit 603 into carrier frequencies in the baseband that are converted into three frequencies of fc ₂ −fd, fc ₂ , and fc ₂ + fd. Here, fc ₂ = fc−1 / (2T). fc ₂ corresponds to 402b in FIG. 4, fc ₂ −fd corresponds to 402c, and fc ₂ + fd corresponds to 402a.

<Receiving method of high rate carrier>
Next, a method for receiving a high rate carrier will be described.
FIG. 7 is a diagram illustrating the multicarrier demodulation unit 121 in more detail. The received multicarrier signal is amplified by the front end unit 701 and converted into a baseband signal. The baseband signal is converted into a digital signal sequence through an A / D converter.

  The converted digital signal sequence is converted into parallel data of N samples for each symbol by a serial / parallel converter 702. These parallel data are subjected to filter processing by a band limiting unit 703 having the same configuration as the band limiting unit 505 shown in FIG. In the band limiting unit 703, the filter processing is performed by the filter 705 via the delay memory 704 having the symbol length T. The band limiting unit 703 performs a filter process equivalent to applying a band pass filter in units of subcarriers. The filter characteristic, that is, the impulse response of the filter 705 can be a matched filter corresponding to the filter characteristic of the filter 507 of the band limiting unit 505.

  Note that the filter processing does not necessarily need to be a matched filter, and may be a filter having a pass bandwidth substantially equal to the subcarrier interval. For example, when an impulse response of a Gaussian function is used, intersymbol interference is reduced by slightly shortening the Gaussian pulse width. Therefore, if the delay spread is large, the characteristics may be improved by shortening the pulse width.

  The filtered signal is converted into a modulated signal for each subcarrier by an FFT converter 707. Thereafter, the operation is exactly the same as that of a conventional OFDM receiver or OFDMA receiver. The signal is demodulated by the demodulator 708 and converted to the original data through a demapping unit 709 and a parallel / serial converter 710 that perform processing reverse to the subcarrier mapping of the transmitter.

<Receiving method of low rate carrier>
As for the configuration of single carrier demodulator 122 (low-rate carrier reception method) in FIG. 1, a conventional single signal is received by receiving three frequencies fc ₁ and fc ₁ ± fd and combining the demodulated output with diversity. Since it is the same as the signal processing of the carrier receiver, the description is omitted.

<Multi-carrier terminal>
Since the multi-carrier terminal TM is a master station apparatus B that omits functions related to transmission / reception of a single carrier, a description thereof will be omitted.

<Dedicated terminal for low rate carrier>
In the description so far, the transmission / reception method by the master station apparatus B has been mainly described. Next, a transmission / reception method using a low-rate carrier dedicated terminal will be described.

FIG. 8 is a diagram illustrating the configuration of the single carrier terminal TS. The receiving circuit and demodulating means in FIG. 8 are the same as those of the conventional single carrier receiver, and receive the carrier frequency fc ₁ or fc ₂ . Note that fc ₁ and fc ₂ are the center frequencies (fc + 1 / (2T) or fc−1 / (2T)) of the low-rate carrier transmitted by the master station device B. In the present embodiment, a single carrier terminal TS1 is the carrier frequency fc _1, as a single carrier terminal TS2 receives the carrier frequency fc _2, illustrating the frequency of TS1 example.

  A received signal from the antenna 801 is input to the receiving circuit via an antenna switching unit 802 that is a duplexer equivalent to the antenna switching unit 102 and a mixer 803 as a frequency conversion circuit. In the mixer 803, the signal is mixed with the local signal having the frequency fd generated by the local oscillator 804. There are several types of mixer configurations depending on the circuit. Here, the sum and difference of the input signal frequency and the local signal frequency, and the input signal appearing at the output are used. The mixer 803 may be, for example, a source injection mixer that adds an input signal and a local signal to the input of a common source FET (field effect transistor) amplifier circuit, or a balanced differential input to an input port of a balanced modulation circuit such as a Gilbert cell mixer. A circuit with a slightly unbalanced degree may be used. These are very common high frequency circuits.

Here, it is assumed that three frequencies of frequency fc ₁ and fc ₁ ± fd are input to the mixer 803. The output from the mixer, the sum and difference of the input signal frequency and the local signal frequency, and since the input signal appears at the output, the input component of fc ₁ to frequency components of fc ₁ and fc ₁ ± fd in the output port, fc the input component frequency components of _fc 1, _fc 1 + fd and _fc 1 + 2fd of ₁ + _fd, input components of fc 1 -fd appear are transformed into frequency components of _{fc 1, fc} 1 -fd and _fc 1 _-2fd. That is, all three received signals having frequencies of fc ₁ and fc ₁ ± fd are converted to frequency fc ₁ .

The receiving circuit may receive frequency fc ₁ is set. In other words, the other frequency components are removed, and the signals of the three frequency components are superimposed and added around fc ₁ and received. As described above, in the single carrier modulation signal generation unit 112 in the master station apparatus B, these three frequency components are phase-controlled so as to be in phase, so these signals strengthen each other, and the maximum ratio synthesis or It becomes frequency diversity reception of equal gain synthesis. Since the phase control is performed on the master station device B side, diversity reception can be performed on the terminal side simply by adding a mixer circuit and a local oscillator to a normal single carrier receiving circuit.

In the master station device B, the transmission frequency of the low-rate carrier can be set to fc ₂ or the like other than fc ₁ , but even if the carrier frequency is different, reception by the single carrier terminal is possible. It goes without saying that the logic is similar.

The present embodiment is a TDD wireless system that transmits and receives at the same frequency by time division, but FDD (Frequency Division Duplex) that transmits and receives at different frequencies simultaneously.
It can also be used for systems. In this case, the antenna switching unit 102 in FIG. 1 and the antenna switching unit 802 in FIG. 8 serve as an antenna duplexer (duplexer).

Next, a method for transmitting a low-rate carrier using the configuration of the single carrier terminal TS shown in FIG. 8 will be described. The modulation means and the transmission circuit are the same as those of the transmission apparatus in the conventional single carrier radio, and transmit the carrier frequency fc ₁ or fc ₂ . A mixer 805 as a frequency conversion circuit is connected to this output. The operation of the mixer 805 is the same as that of the mixer 803 described in the reception operation. Therefore, three frequency components of fc ₁ and fc ₁ ± fd or fc ₂ and fc ₂ ± fd are output in the same phase to the output of the mixer 805 and transmitted from the antenna to the master station apparatus B. That is, by adding an equivalent mixer circuit for transmission, the same frequency diversity effect as that during reception can be obtained.

(Second embodiment)
In the second embodiment, MIMO communication is performed using the master station device B and the single carrier terminals TS1 and TS2.
FIG. 9 is a diagram illustrating the relationship between the wireless communication device and the terminal in the second embodiment. In the present embodiment, communication is performed with the master station apparatus B using two single carrier terminals TS1 and TS2. Here, the single carrier terminal is referred to as a slave station device.

The slave station devices TS1 and TS2 have the same configuration as that described in the first embodiment. However, in this embodiment, the frequency assigned to these slave station devices TS1 and TS2 is common, and a case will be described in which communication is performed using the same spectrum of fc ₁ and fc ₁ ± fd. In FIG. 9, H ₁ (f) and H ₂ (f) are the slave station devices TS at the frequency f.
1 represents a transfer function of a transmission path (propagation path) from TS2 to the master station device.

x _{1, x 2} represents respectively a baseband signal of the transmission signal in the slave station device _{TS1, TS2, y 1, y} 2, y 3 , the frequency fc ₁ and _fc 1 + fd of the received signals in the parent station, fc ₁ Represents the baseband signal of the received signal in the −fd spectrum, respectively. It should be noted that the baseband signal of the transmission signal in terminals TS1 and TS2 is common in the spectrum at any frequency of fc ₁ and fc ₁ ± fd, as is apparent from the configuration of FIG.

The operation of the communication system configured as described above will be described below. The transmission signals x ₁ , x ₂ from the slave station devices TS 1 and TS ₂ and the reception signals y ₁ , y ₂ , y ₃ at the master station device have the relationship described in Equation 2.

This is rewritten as Equation 3. Here, the column vector of x ₁ and x ₂ is set as x, and y ₁ ,
A column vector of y ₂ and y ₃ is set as y, and a matrix of 3 rows and 2 columns on the right side of Equation 2 is set as H. Since the signal mix of x ₁ and x ₂ is the received signal of the master station can not receive interfere with each other in this state. Therefore, when the master station apparatus estimates H and multiplies the generalized inverse matrix H ⁺ of H from the left of both sides as shown in Equation 4, H ⁺ H becomes a value close to a unit matrix of 2 rows and 2 columns. By performing the weighted addition according to the generalized inverse matrix of H with respect to the three received signals y, x ₁ and x ₂ are obtained is separated. That is, H is determined so that the ratio of the power of the desired signal and the power of the undesired signal, that is, the interference signal is minimized. This signal processing is called zero forcing.

  Such a technique for separating and demodulating a signal from a plurality of signals superimposed on a plurality of transmission paths is called MIMO, and there are several types of signal processing methods such as MMSE (Minimum Mean Squared Error) in addition to zero forcing. Are known. When MMSE is used, the weighting and addition weights may be controlled so that the ratio of desired signal power to the sum of interference signal power and noise signal power is maximized. Also, other than zero forcing and MMSE, other algorithms such as MLD (Maximum Likelihood Detection) may be used as long as they are signal processing methods capable of obtaining a multiplex transmission effect. These signal processing methods are disclosed in, for example, a standard technology collection “MIMO (Multi Input Multi Output) related technology” published on the Japan Patent Office WEB site.

  The MIMO in the present embodiment is different from the conventional MIMO in the following points. That is, in conventional MIMO communication, spatial multiplexing transmission is performed at the same frequency using a plurality of terminals as slave station devices and a plurality of antennas included in the master station device. On the other hand, in the second embodiment, a MIMO transmission path can be formed with a single antenna using a plurality of terminals that are slave station devices and a plurality of frequencies.

Next, a case where data is transmitted from the master station device to the slave station devices TS1 and TS2 will be described. Similarly in the reverse direction, it is possible to transmit two signals destined for different terminals at the same frequency. Hereinafter, description will be made with reference to Equation 5. y _d1 and y _d2 are the baseband signals of the received signals at the slave station devices TS1 and TS2, respectively. x _d1 , x _d2 and x _d3 are the frequencies fc ₁ , fc ₁ + fd and fc ₁ -fd of the master station device, respectively. Represents the baseband signal of the transmitted signal in the spectrum.

H ^T is a transpose matrix of H, and Equation 6 is obtained by rewriting y _d1 , y _d2 , and x _d1 , x _d2 , x _d3 to column vectors, respectively. When s ₁ and s ₂ are baseband signals of transmission signals directed to the slave station devices TS1 and TS2, respectively, and the column vector _xd is expressed by Equation 7, the relationship of Equation 8 is obtained.

That is, if _xd is generated and transmitted by the signal processing indicated by the same equation, only _one of s ₁ and s ₂ can be dominantly received on the slave station side. In this case, the slave station devices TS1 and TS2 do not particularly require computation for signal separation, and are performed by the frequency conversion circuit shown in FIG.

  As described above, according to the present embodiment, complicated signal processing in the terminal device is not required, and a master station device and a slave station device suitable for a small sensor terminal and a communication system using them can be provided.

(Modification)
The above embodiment is merely an example, and the present invention can be implemented with appropriate modifications within a range not departing from the gist thereof. For example, in the description of the embodiment, three null carriers have been described, but another set of null carriers may be provided at a position further away from the center frequency, and a total of five may be provided. Further, another communication may be performed using a plurality of low rate carriers without using frequency diversity.

  Further, the symbol rate used for single carrier communication does not need to be ½ of the symbol rate used for multicarrier communication, and may be arbitrary.

  In the above description, transmission / reception processing is performed between the master station device and the multicarrier terminal, and between the master station device and the single carrier terminal. It does not matter even if it communicates. As an example, the master station device and the multicarrier terminal perform transmission / reception, but the single carrier terminal may transmit only to the master station device. Even in such a case, the advantageous effects described above can be obtained.

Further, the spatial multiplexing transmission in the second embodiment may be performed using only the master station device and the single carrier terminal without using the multicarrier terminal. Even in such a case, it is possible to form a MIMO transmission path with a single antenna using a plurality of terminals that are slave station devices and a plurality of frequencies.

Further, in a single carrier terminal, the frequency converter (mixer) outputs frequency of fc ₁ + fd, fc ₁ , fc ₁ -fd with the input frequency as fc ₁ as an example. Explained that it is obtained. However, even if the mixer of the single carrier terminal is configured to output only two frequencies of fc ₁ + fd and fc ₁ −fd with respect to the input frequency fc ₁ , the diversity effect and the MIMO effect can be obtained similarly. it can.

  Further, in the description of the embodiment, an example in which one master station device communicates with a slave station device has been described, but by controlling so that the frequencies of carriers to be used do not overlap, a plurality of master station devices It is also possible to arrange a combination of slave station devices within the communication range of each other.

B ... Wireless communication device (master station device)
DESCRIPTION OF SYMBOLS 101 ... Spectrum control part 102 ... Antenna switching part 103 ... Antenna 111 ... Multicarrier modulation signal generation part 112 ... Single carrier modulation signal generation part 113 ... D / A converter 114, 124 ... Amplifier 121 ... Multicarrier demodulation part 122 ... Single Carrier demodulation unit 123 ... A / D converter TM1, TM2 ... multi-carrier terminal (slave station device)
TS1, TS2 ... Single carrier terminal (slave station)
301, 302 ... Null carrier 401, 402 ... Low rate carrier

Claims (15)

First communication means for performing at least one of transmission and reception using a multicarrier signal composed of a plurality of subcarriers shaped by a band-limited pulse waveform;
Second communication means for performing transmission and / or reception using a signal with a modulation format or modulation constant different from that of the first communication means;
Have
The first communication means performs communication without using at least one of the plurality of subcarriers,
The second communication means performs communication using a subcarrier band that is not used by the first communication means.
A wireless communication apparatus. The subcarrier symbol used by the first communication means is asynchronous with the carrier symbol used by the second communication means.
The wireless communication apparatus according to claim 1, wherein: The first communication means performs communication without using two or more subcarriers of the plurality of subcarriers,
The second communication means is
The first communication means communicates the same signal in a frequency band of a subcarrier not used for communication,
Send weighted signals in each frequency band, or select and send signals in any frequency band.
The wireless communication apparatus according to claim 1, wherein the wireless communication apparatus is a wireless communication apparatus. The second communication means weights and transmits the signals of the plurality of frequency bands so that the signals of the plurality of frequency bands have the same phase at the antenna input of the transmission destination terminal.
The wireless communication apparatus according to claim 3. The second communication means transmits signals in three frequency bands fc + fd, fc, and fc−fd having the same frequency interval.
The wireless communication apparatus according to claim 3, wherein the wireless communication apparatus is a wireless communication apparatus. The first communication means performs communication without using two or more subcarriers of the plurality of subcarriers,
The second communication means performs transmission to a plurality of terminals using a transmission signal in a frequency band possessed by a subcarrier that is not used for communication by the first communication means,
Weighting and combining data addressed to the plurality of terminals based on propagation path characteristics to determine a transmission signal for each frequency band;
The wireless communication apparatus according to claim 1, wherein the wireless communication apparatus is a wireless communication apparatus. The second communication means weights and transmits so that data addressed to the terminal is dominantly received at the antenna input of the plurality of terminals.
The wireless communication apparatus according to claim 6. The first communication means performs communication without using two or more subcarriers of the plurality of subcarriers,
The second communication means receives a signal using a frequency band of a subcarrier that the first communication means does not use for communication,
In each frequency band, a signal of the same data is transmitted from the transmission source,
The second communication means receives and weights and synthesizes the signals of each frequency band, or selects and receives a signal of any frequency band,
The wireless communication apparatus according to claim 1, wherein: The first communication means performs communication without using two or more subcarriers of the plurality of subcarriers,
The second communication means receives signals from a plurality of terminals using a frequency band possessed by a subcarrier not used for communication by the first communication means,
Each of the plurality of terminals transmits signals in a plurality of frequency bands;
Extracting signals transmitted from each terminal by weighting and combining signals received in each frequency band based on propagation path characteristics,
The wireless communication apparatus according to claim 1, wherein the wireless communication apparatus is a wireless communication apparatus. Receiving means for receiving signals of a plurality of frequency bands transmitted from the second communication means of the wireless communication device according to any one of claims 3 to 5;
Frequency conversion means for converting the frequency of the input signal;
Have
A plurality of frequency band signals received by the receiving means are converted into a common frequency band by the frequency converting means;
A wireless communication apparatus. Receiving means for receiving signals in frequency bands fc + fd, fc, fc-fd transmitted from the second communication means of the wireless communication device according to claim 5;
A frequency conversion means for frequency-converting an input signal, which outputs a signal on which an input signal, a signal obtained by frequency-converting the input signal by frequency + fd, and a signal on which the signal obtained by frequency-converting the input signal by frequency -fd is superimposed Conversion means;
Have
The radio communication apparatus according to claim 1, wherein the receiving unit superimposes and adds the signals in the frequency bands fc + fd, fc, and fc−fd to the frequency band fc by the frequency converting unit. A wireless communication system including a master station device, one or more multicarrier terminals, and one or more single carrier terminals,
The master station device is
First communication means for communicating with a multicarrier terminal using a multicarrier signal composed of a plurality of subcarriers shaped by a band-limited pulse waveform;
Second communication means for performing communication using a signal with a modulation format or modulation constant different from that of the first communication means;
Have
The multicarrier terminal has communication means for communicating with first communication means of the master station device,
The single carrier terminal has communication means for communicating with second communication means of the master station device,
In communication between the master station device and the multicarrier terminal, communication is performed without using at least one of the plurality of subcarriers,
In communication between the master station device and the single carrier terminal, communication is performed using a subcarrier band that is not used for communication between the master station device and the multicarrier terminal.
A wireless communication system. A wireless communication system including a master station device and a plurality of terminals,
The master station device transmits signals to a plurality of terminals using signals in a plurality of frequency bands, and weights and synthesizes data addressed to the plurality of terminals based on propagation path characteristics to transmit each frequency band. Having a transmission means for determining a signal;
The terminal includes a receiving unit that synthesizes and receives signals of each frequency band transmitted from the transmitting unit of the master station.
A wireless communication system. The transmission unit of the master station device transmits the weighted data so that data addressed to the terminal is dominantly received at the antenna input of the plurality of terminals.
The wireless communication system according to claim 13. A wireless communication system including a master station device and a plurality of terminals,
Each of the terminals includes a transmission unit that transmits a signal to the master station apparatus using a plurality of frequency bands.
The plurality of frequency bands are common to the plurality of terminals,
The master station device has receiving means for extracting signals transmitted from each terminal by performing weighted synthesis based on propagation path characteristics of signals received in the plurality of frequency bands,
A wireless communication system.

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